The present invention provides a structure in which rods which are used in a rod mill, are allowed to rotate in parallel with the axis of rotation of an ore grinding machine (hereinafter referred to as a rod mill), without being bent.
A rod mill has its internal circumference lined with liners, and rotates after ore and rods are put in, and crushers and grinds ore (hereinafter simply referred to as grinds), with the rods rolling on the liners. Among various types of rod mills, there is a mill of the central circumference discharge type in which ore is fed from two end ports of its main body and crushed ore is discharged from the central circumference. FIG. 1 shows the liner assembly of a main body of such a mill of the central circumference discharge type, with the cylindrical main body cut along the line A--A' or B--B' and stretched over a flat surface, where the side edges A--A' and B--B' are seemlessly butted to form a cylinder with its ends respectively formed into a circle by the edges A--B and A'--B'. As seen in the developed view of the main body liner assembly in FIG. 1, the liners or first liner members 1 are arranged in a plurality and in parallel throughout the inner circumference of the main body, and the liners or second liner members 3 which have discharge ports 2 are arranged along the circumference of a center portion of the main body. The liners 3 having the discharge ports may be arranged either side by side as shown in FIG. 1 or with several liners 1 interposed therebetween along the circumference. The liners 1 arranged throughout the main body are integrally formed at their liner bases 4 with lifters 5 which push ore and rods (both not shown in the drawings) up. This applicant has worked out several patented inventions of liners 1 with lifters 5 which are based on the rod mill liners disposed in Japanese Pat. No. 574,843 and the rod mill liners of the aforementioned invention are also utilized in the present invention. The present invention will be explained hereunder with reference to FIG. 6. In the present invention, the shape and the location of lifter 5 relative to a liner base 4 are so selected that the top of the lifter is shifted adjacent the attaching hole 6 of the liner when the lifter 5 reaches its wear limit, by positioning the lifter forward, with respect to the attaching hole 6 of an attaching bolt (not shown) in the direction of rotation of the rod mill by a distance which is determined by using a certain ratio of the rod diameter as a measure, with the aim to prolong the life of the liners and maintain ore grinding efficiency of the rod mill.
There are peculiar phenomena in the progress of wear of liners by grinding ore in a rod mill of the central circumference discharge type, regardless of the use of liners with either the lifters 5 of said invention or different lifters which are not relating to said invention. The phenomena are illustrated in FIG. 2 which is an enlarged end view of the B--B' edge in FIG. 1. In the liner 3 with central discharge port and in the liners 1 which are arranged on both sides of the liner 3 towards the ends of the mill main body, the wear of the liner bases 4 is shown by the chain line a and that of the lifters 5 is shown by the chain line b. The chain lines a and b show the conditions of wear when the liners 1 at the extreme ends of the mill reached their wear limit. Those conditions indicate that the liners positioned closer to the ends show more wear than the liners positioned closer to the center of the mill, the wear being caused by rods having a length which is almost the same as the lateral length or width B--B' in FIG. 2. FIG. 3 shows the wear conditions of liners, when central liners 3 with discharge ports 2 are not provided with lifters 5. Contrary to the conditions in FIG. 2, the liners closer to the center show more wear than those closer to the ends. Those wear conditions are the phenomena to be effected by various factors such as the movement of rods which are pushed up together with ore, rolled around or dropped onto the liners while the mill body is rotating, the amount of ore to be ground, the flowing condition of ore in the mill, the rotational speed of the mill, or the like.
In order to understand the cause for those phenomena, the conception of the applicant, who has studying many years in working sites in Japan and abroad, is described hereunder. Considering the grinding and rod motion, rods loaded in a mill are pushed up by lifters in the direction of rotation, flow and fall down in repetitive manner during the rotation of the mill, and the loaded ore is gradually ground down, with the rod motion being effected mostly by the lifters on the liners. A rod in motion is not kept in parallel with the rotational axis of the mill while it is being pushed up, flows and falls down, but has its ends twisted, or its whole length bent, taking various shapes in motion. Considering the wear of liners and rods, the liners positioned in the ore feeding side wear more than other liners in almost every case, though little difference is observed depending on the type and construction of the rods and the kind and content of ore to be ground. Further, a rod shows such irregular wear that the center portion of 90 mm in original diameter wears to about 40 mm in diameter while the end portions wear to such an extreme condition that they look like spearheads. Considering the wear of liners and rods and the grinding effect of rods, the grinding of raw materials are accomplished by impact taking place between two rods or between a rod and liners, therefore, the grinding action would progress smoothly and the amount and quality of the ground ore would be kept steady, if the liners and the rods could wear while keeping their original profiles. However, due to the irregular motion of rods in a mill, parts of the rods and liners (including lifters if applicable) wear to the extreme, rendering a decrease in quantity and a deterioration in quality of grinding usually being inevitable. Thus, it is conventional in this industry that the operation of a mill must be stopped for certain days to replace worn liners with new ones by letting workers in the mill to perform replacement operations manually, whenever part of the liners have worn to the limit. This means waste of time in service in that all of the liners must be replaced even though most of them are in a serviceable condition.